Subject: Padding in RTP

From: Murthy Nanduri <[email-masked]>
Date: Wed, 27 Oct 1999 16:46:08 +0900

Hi,

I am working on the implementation of RFC2508.i.e., the
RTP/UDP/IP Header compression and decompression.

I have tested my implementation, with an equipment which
sends the RTP packets with the Marker bit and Padding bits
NOT set. The implementation is working fine and I could able
to hear the voice properly between the two machines.

When I started testing the CRTP implementation with another
equipment which sends the RTP packets with the Marker bit and
Padding bits SET(for some packets of stream), I am unable to hear the
voice between the two machines.

As per the RFC2508, I am setting the Bitmask for the Marker bit while
sending the compressed RTP packet.

When the padding bit is set, I am sending the compressed UDP packet..

Can you please let me know what has to be done by CRTP
with the padding bytes?

I want to know whether the padding bytes have to be removed
by CRTP compressor/decompressor OR it is the responsibility
of the RTP applications to ignore the padding bytes..

I think it is the responsibility of the Voice applications to take care
of the
padding bytes.. Am I right?

can U please let me know what for the Marker bit and Padding bits are
used?

Murthy NVN

---

From: Stephen Casner <[email-masked]>
Date: Fri, 29 Oct 1999 00:07:09 -0700 (Pacific Daylight Time)

> RTP/UDP/IP Header compression and decompression.
...
> sending the compressed RTP packet.

Right.

> When the padding bit is set, I am sending the compressed UDP packet..

If the padding bit is set on all the packets, then you should be able
to still send them as COMPRESSED_RTP packets.  You only need to send
COMPRESSED_UDP when the P bit changes (since there is no way to
indicate that in a COMPRESSED_RTP packet).

> Can you please let me know what has to be done by CRTP

Nothing.  They should be passed through just as they are, along with
the rest of the payload.

> of the RTP applications to ignore the padding bytes..

The answers are no and yes.  A properly operating RFC2508 compressor
and decompressor will produce packets at the output of the
decompressor which are identical to the packets as they went into the
compressor.

> can U please let me know what for the Marker bit and Padding bits are

This is explained in the RTP spec (RFC 1889 or draft-ietf-avt-rtp-new-07)

							-- Steve